This is a known issue. We pushed a fix earlier this week, but it’s not resolving itself automatically for some reason. However, if you speak to an Apprentice Watcher in Orgrimmar, Undercity, or Ironforge and remove and then re-add the Soul of Iron buff by going through the “What do my stories tell?” option, that should clear it up and pick up the fix.
Edit: In theory, if you choose the option to remove self-found after reaching level 60, this shouldn’t matter; you’re still flagged as reaching level 60 as self-found. However, as Azeroth mentioned below, it’s probably safest not to select that option.